// Frequency Measurement - Arduino Nano (Leading Edge Detection)

#define SENSOR_PIN 5  
#define SECOND 1000000
#define SEC_PER_MIN 60

float lastTime = 0;
float frequency = 0;
bool lastState = 0;


void setup() {
  pinMode(SENSOR_PIN, INPUT);
  Serial.begin(9600);
  delay(1000); // Allow Serial Monitor to initialize
}

void loop() {
  float currentTime = micros();
  bool currentState = digitalRead(SENSOR_PIN);
  // Leading edge detection
  if ((lastState == 0)&&(currentState == 1)) {
    frequency = SECOND/(currentTime-lastTime);
    Serial.print("RPM = ");
    Serial.println(frequency*SEC_PER_MIN);
    lastTime = currentTime;
  }
  lastState = currentState;
}